Hurricane Glossary

air pressure Air pressure is the weight of the column of air that extends from the ground (or water's surface) to the top of the atmosphere. Air pressure is also called barometric pressure; it is measured by a barometer. The air pressure is very low in a hurricane.

anemometer An anemometer is a weather instrument that measures wind speed.

Atlantic Ocean The Atlantic Ocean is a large body of salt water that separates the Americas from Europe and Africa. It is the second largest ocean.

barometer A barometer is a device that measures air (barometric) pressure. It measures the weight per square inch of the column of air that extends from the instrument to the top of the atmosphere. Falling barometeric pressure usually means that a storm is coming.

barometric pressure Barometric pressure is the weight of the column of air that extends from the ground (or water's surface) to the top of the atmosphere. It is also called air pressure. Air pressure is measured by a barometer. 29.92 is the average air pressure at sea level. Barometric pressure is very low in a hurricane.

counterclockwise Counterclockwise motion goes in a circle in the opposite direction from the way a clock moves. Hurricane winds blow in a counterclockwise direction.

cyclone A cyclone is a closed, rotating wind. Cyclones rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

degree A degree is a unit of measurement of an angle; a degree is also written °. There are 360 degrees in a circle. Each degree is divided into 60 minutes, written as the symbol '. For example, 10 and a half degrees is written 10° 30'. Latitude and longitude are in measured in degrees.

Equator The Equator is an imaginary circle around the Earth, halfway between the North and South Poles.

eye Hurricane winds blow in a spiral around the calm, roughly circular center called the eye. In the eye, which is about 20 - 30 miles wide, it is relatively calm and there is little or no rain. The eye is the warmest part of the storm.

eyewall Also called the wall cloud. Surrounding the eye is the eyewall, a band of thunder clouds. The eyewall has the most rain and the strongest winds of the storm, gusting up to 225 mph (360 km/h). The smaller the eye, the stronger the winds.

forecast A forecast is a prediction of future weather made by meteorologists.

hurricane A hurricane is a powerful, rotating storm that forms over warm oceans near the equator in the Atlantic Ocean, the Caribbean Sea, or the eastern Pacific Ocean. Hurricanes have strong, counterclockwise winds (at least 74 miles per hour or 119 kph), a huge amount of rain, low air pressure, thunder and lightning.

hurricane classification Hurricanes are classified into five categories, based on wind speed (using the Saffir-Simpson scale). Category 1 -- Winds 74-95 mph Category 2 -- Winds 96-110 mph Category 3 -- Winds 111-130 mph Category 4 -- Winds 131-155 mph Category 5 -- Winds over 155 mph.

hurricane season Hurricane season is from June 1 until November 30, when most Atlantic Ocean hurricanes occur. In the eastern Pacific Ocean, hurricane season is from May 15 until November 30.

Hurricane Warning A hurricane warning means that a hurricane is expected in the warning area within 24 hours or less.

Hurricane Warning marine flags The marine flags that warn of a hurricane are two square red flags, each with a black square in the middle.

Hurricane Watch A hurricane watch means that a hurricane is possible in a given area within 36 hours.

International Date Line The International Date Line (IDL) is an imaginary north-south line (at the 180th meridian), in the Pacific Ocean, at which the date changes. The east side of the IDL is a calendar day earlier than the west side. The actual IDL used is not a straight line, but zigzags around certain populated areas.

latitude Latitude is the angular distance north or south from the equator to a particular location. The Equator has a latitude of zero degrees. The North Pole has a latitude of 90 degrees North; the South Pole has a latitude of 90 degrees South.

longitude Longitude is the angular distance east or west from the north-south line that passes through Greenwich, England, to a particular location. Greenwich, England, has a longitude of zero degrees. The farther east or west of Greenwich you are, the greater your longitude. The Midway Islands (in the Pacific Ocean) have a longitude of 180 degrees (they are on the opposite side of the globe from Greenwich).

meteorology Meteorology is the science that deals with weather. A scientist who studies weather is called a meteorologist.

National Hurricane Center The National Hurricane Center is a US government organization that tracks hurricanes in the Atlantic, Caribbean, Gulf of Mexico and eastern Pacific, and issues advisories about the storms.

Northern Hemisphere The Northern Hemisphere is the half of the Earth that is north of the equator.

nowcast A nowcast is a prediction of the weather likely in the immediate future (the next few hours) made by meteorologists.

overcast When the sky is overcast, clouds cover the sky.

precipitation Precipitation is water in all forms that falls from clouds to the earth's surface, including rain, snow, sleet, and hail.

Southern Hemisphere The Southern Hemisphere is the half of the Earth that is south of the equator.

spiral rainbands Spiral rainbands are long bands of rain clouds that seem to spiral into the eyewall.

storm surge A storm surge is a rise in the ocean as the result of strong winds from a hurricane or other intense storm. A storm surge can cause dangerous flooding, especially when a storm surge coincides with a high tide. The height of the storm surge waters is the difference between the level of the ocean and the level that would have occurred normally. A storm surge is usually estimated by subtracting the regular high tide level from the observed storm tide - it can be 15 feet tall or more.

storm tide A storm tide is the observed level of sea water. It is a result of the normal tide plus the storm surge.

Storm Warning marine flag The marine flag that warns of a hurricane is one square red flag with a black square in the middle.

Tropic of Cancer The Tropic of Cancer is an imaginary line of latitude at 23°30' N.

Tropic of Capricorn The Tropic of Capricorn is an imaginary line of latitude at 23°30' S.

tropical cyclone A tropical cyclone is a violent low-pressure weather system in which the central core is warmer than the surrounding winds. If it forms in the Atlantic or eastern Pacific Ocean, it is called a hurricane. If it forms in the western Pacific Ocean, it is called a typhoon.

tropical depression A hurricane goes through many stages as it develops. As the air pressure drops and there are sustained winds up to 38 miles per hour, it is called a tropical depression.

tropical disturbance A hurricane goes through many stages as it develops. As the warm, moist air over the ocean rises in the low air pressure area, cold air from above replaces it. This produces strong gusty winds, heavy rain and thunderclouds that is called a tropical disturbance.

tropical storm A hurricane goes through many stages as it develops. When the cyclonic winds have sustained speeds from 39 to 73 miles per hour, it is called a tropical storm.

tropical wave A hurricane goes through many stages as it develops. It starts as a tropical wave, a westward-moving area of low air pressure.

tropics The tropics are the warm, equatorial region between the Tropic of Cancer and the Tropic of Capricorn.

troposphere The troposphere is the lowest region in the Earth's (or any planet's) atmosphere. On the Earth, it goes from ground (or water) level up to about 11 miles (17 kilometers) high. The weather and clouds occur in the troposphere. In the troposphere, the temperature generally decreases as altitude increases.

typhoon A typhoon is a tropical cyclone that forms in the Western Pacific Ocean (west of the International Date Line).

updraft An updraft is a current of air that is flowing upwards.

vortex A vortex is a spinning flow of air.

waterspout A waterspout is a tornado that passes over water. It is a funnel-shaped formation of wind, water and ocean spray.

weather map A weather map is a map that shows weather conditions for a given time. Weather maps show storms, fronts, temperatures, rain, snow, sleet, fog, etc.

weather satellite A weather satellite is an orbiting machine that takes pictures of the Earth's surface that are used for noting the Earth's weather.

Hurricanes

Introduction to Hurricanes

How Hurricanes Form

Naming Hurricanes

Hurricane Structure

Hurricane Classification

Tracking Hurricanes

Preparing for a Hurricane

Landfall, Storm Surges

Hurricane Activities

Hurricane Glossary

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